Tolkien, Asimov, Card & Choose your own Advent (Score 1)

They've already been mentioned but:

The Hobbit (not Sci-Fi) got me hooked in 6th grade. I read LotR in 7th & 8th. Hooked forever.

I, Robot (not the movie!). I think I've still got the copy dated in the 60's that I got from my Dad. The rest of the Robot Stories are a good follow on.

Ender's Game is another one that I've read many times since Jr. High.

Not mentioned (that I saw):

Choose your own Adventure. If you can find them, these are some of the best books ever. There are lots of Time Travel and Sci-Fi stories in there. A game and a book. What more can you ask for?

On a Pale Horse from Piers Anthony is a good novel that starts with an odd premise and leads to a few more good books.